Hydrogen gas generators are known wherein hydrogen gas is generated by, e.g., a reaction between ammonia (NH3) and a solid reactant such as lithium aluminum tetrahydride. The resulting hydrogen gas is generally contaminated with ammonia which must be filtered from generated hydrogen gas stream prior to this stream entering a device (e.g., a fuel cell, a gas chromatograph, or a flame ionization detector) that uses hydrogen. Only trace amounts of ammonia are contained in the generated gas mixture up until the generator is substantially depleted of its ability to generate hydrogen gas. Such trace amounts of ammonia can be filtered from the generated gas by providing a material or substance (denoted a “getter” or “getter material” herein) that extracts the ammonia from the generated gas. Prior techniques for performing such filtering of chemical contaminants such as ammonia from contacting the anode of a fuel cell have included direct particle filtration combined with a consumable getter material as shown in U.S. Pat. No. 6,274,093, filed Aug. 6, 1998 and incorporated fully by reference herein. Successful getter materials for the removal of ammonia have included an adsorption material such as zeolite, activated charcoal and/or sodium hydrogen sulfate monohydrate (NaHSO4.H2O). Note that NaHSO4.H2O reacts chemically with and permanently traps NH3 from the H2 stream.
However, when the hydrogen generating reaction within the generator approaches the end of the reaction's ability to generate hydrogen, the concentration of ammonia (or other contaminant) in the generated gas can increase abruptly and substantially. Such an increase in a contaminant (e.g., ammonia) concentration is denoted herein as a “breakthrough.” Moreover, such a breakthrough will eventually overcome the ability of the getter material to filter the contaminant from the gas stream since the getter becomes spent or saturated from reactions with the contaminant in the H2 stream. Accordingly, the contaminant in the gas stream will accumulate and, at least in the case of ammonia, disable the device receiving the hydrogen gas stream unless the high concentrations of ammonia are prevented from entering the device.
Accordingly, it would be desirable to have a method and apparatus that would inhibit passage of the NH3 contaminated hydrogen into the hydrogen consuming device by stopping the H2 and NH3 gas mixture flow once there is ammonia breakthrough into the generated gas stream. It would also be desirable provide getter materials with large capacities for trapping NH3 for thereby extending the effective operating time and total hydrogen delivered from a hydrogen gas generator. Moreover, it would be desirable for such a method and apparatus to detect changes in the gas stream NH3 concentration, and/or rate of concentration change in simple, reliable, and cost effective manner. Additionally, in at least some contexts it would be desirable for the method and apparatus to be substantially passive in the sense that a chemical reaction between the breakthrough ammonia and a breakthrough detection material can, e.g., plug the line providing the generated gas stream so that the gas stream ceases to flow into the device. It would also be advantageous to prevent passage of any unwanted gas to a feed gas consuming device that might not consume hydrogen.